Synchronizing generator



Sept.1s, 1945. R E KESSLER- 2,384,931

SYNCHRON I Z ING GENERATOR Filed Jan. 14. 1942 lill Patented Sept. 18, 1945 UNITED STATES PATENToFFIcE Robert E. Kessler, Upper Montclair, J.,`assignor to Allen B. Du Mont Laboratories, l.nc., Passaic, N. J., a corporation of Delaware Application January 14, 1942,1SeralNo.-`426,695 1 clam.A (c1. 250436) This invention relates to a synchronizing generator that is particularly useful in television. By it, simplified circuits and very flexible switching are provided. The generator is very stable,A even when operating at several widely different frequencies of line and eld scanning. It can be made of light weight and small size so that it is readily portable, and, at the same time it is ad# justable to a wide range of line and frame scanning standards. A cathode-ray tube of the builtin type is provided for monitoring, and both horizontal and vertical linearity test bars forthe Pattern are made available.

This invention relates to the production of. sweep and blanking signals for iconoscopes, blanking pedestals for Video amplifiers,` and corn-` posite super-synchronizing signals. Sweep voltages are also supplied to auxiliary equipment, and test signals are supplied for checking sweep linearity.

In carrying out the invention a vacuum tube is caused to operate as a sine-Wave oscillator at twice the desired line scanning frequency for an iconoscope. A second tube is caused to operate as a relaxation oscillator and is synchronized by the sine Wave of the first tube so as to produce a pulse at the frequency of this sine wave, which frequency will be called the master .frequencyi This pulse of master frequency is used to synchronize another vacuum tube oscillator at half the frequency, thus producing a pulse at the desired line frequency.

The pulse at line frequency is used as a driving` pulse for producing sawtooth wave forms as wellas wave forms for super-synchronizing. The: pulse at master frequency is also used to syn-Y chronize a chain of relaxation type oscillators for the purpose of dividing the master frequency down to the desired field scanningV frequency. The pulse at field frequency is used to produce sawtooth sweep wave forms and also wave forms for super-synchronizing. Control tubes interlock the field frequency and power-line frequency to4 the master sine-wave oscillator to keepit at the proper frequency.

The time constants of the oscillator circuits can be quickly changedVA by switching arrangements so that the impedances of circuitsare readily varied to provide the desired frequencies. r c

With this invention, pulses can be introduced into the super-synchronizing circuits so that' the horizontal and vertical sweep wave forms, can be readily tested for linearity, determining camera linearity and receiver linearity independently.' A-

cathode-ray tube for observing the various wave'isf vforms is built in the-generator, with a switch which selects the signal or Wave form to be observed as well as the proper sweep frequency time base for the` respective signals.

The invention may be understood from the description in connection with the accompanying drawing, in which: l

Fig. 1 shows a master pulse generator in which the frequency can be changed;

Fig. 2 shows a pulse generator from which a line frequency pulse suitable for television may showingfhow linearity test signals may be generated; and

Fig. 4 shows the pattern on a television receiver illustrating the linearity test.

K In the drawing, reference character I indicates a wire leading from a sine-wave generator to the transformer 2 of the relaxation oscillator 24 to synchronizev the oscillator 25. One end of the primary 3 is connected through load resistor 4 to ground and the other end is connected through condenser 5 to grid 6 of the oscillator tube 1. Provision is made by means of switch 8 for connecting grid 6 to ground through any one of a series of .resistors 9 which will cause the tube to oscillate at a numberV of desired frequencies that maybe selected, by means of the switch. The small variableresistor I0 is to `adjust the frequency more closely when necessary. The positive 3 side of a source of voltage is connected through the secondary I2 of the transformer 2 tothe plate ISinth'e known way, and the master pulse at the selected frequency is taken on by the lead I4 between. the *cathode 4I5 and resistor I6 which is grounded.v f I .A'signal ati the desired frequency applied by thelead 'I causes `theltube l to oscillate in synchronism ,with it; thus'producing a positive pulse. When-the input signal 'at I is 4a sine wave at master frequency` the output signals at I4 and- I4 are positive pulsesvoccurr-ing at the masterV frequency when theproper `resistor 9 is used. p

In order to obtain a pulse at one-half the masterA frequency, which is the line scanning frequency, the master pulse on I4 is applied to another relaxation oscillator 25 such as shown in Fig. 2. V'I'hle pulse is applied to the primary I5 of the transformer I6'. 'I'he time constants for this oscillator,- which-depend upon the condenser I'I and the resistors I8 in series with the small adjustable resistor I9, are selected so that the frequency of this oscillator 20 is exactly half of the rst one when the master pulse from the first oscillator is applied to it.

In the diagram shown in Fig. 3 a master sinewave oscillator 23 is shown as one which may generate a 31.5 kc. sine wave, for example. A master oscillator control tube 2| is connected to it, which is in turn controlled by direct current from a lock-in circuit 22 connected to the field frequency pulse of 60 cycles. The signal from the 31.5 kc. oscillator 23 which is at twice line frequency is applied to the master pulse oscillator 24, which is the oscillator shown in detail in Fig. 1. The signal from the master pulse oscillator 24 is applied to the oscillator 25, which is shown in detail in Fig. 2, where theY frequency is halved, and is the present standard 15,750 cycles per second, or 525 lines per frame for television line scanning.

The frequency of the signal from the master pulse oscillator 24 is divided 1, 5, 5 and 3 as indicated at 30, 3|, 32 and 33 to provide a pulse at the field frequency of 60 C. P. S., or frame frequency of 30 C'. P. S. with interlaced scanning. It will be understood that the resistances such as resistances 9 (Fig. l) will be inserted in accordance with the frequency of the input signal at At the same time the resistances I8 (Fig. 2) and all-the other corresponding resistances in the oscillators indicated in Fig. 3 at 23, 24, 25, 30, 3|, 32 and 33, will be correspondingly changed. 'Ihese blocks indicate oscillators similar to those shown in Figs. 1 and 2. For changing the resistances in these oscillators, switches 8 and 8' and corresponding switches at the other oscillators indicated in Fig. 3 are connected together or ganged as indicated by the dotted line L (Figs. 1 and 2) so that they will be moved correspondingly and simultaneously, thus providing the needed time constants for the respective oscillators at all times.

In a similar way, pulses at other frequencies such as 441 lines at 30 frames per second or 625 lines at l frames per second, for example, can be obtained. The following table shows suitable data for practical cases:

Master Line lst 2nd 3rd Field Lm? Frame freq. freq. divider divider divider freq.

0.P.s.0.P.sC.P.s0.P.sc.P.s.o.P.s. 441 a0 26,460 13,230 3,780 540 180- 00 525 30 31,500 15,750 4,500 90o 1130v 60 025 18,750 9,375 3,750 750 150 .30

Since the relaxation oscillator 24 (Fig. 1) described herein is very stable, the switching arrangements shown in Figs. 1 and 2 can be safely utilized for quickly changing to different scan-4 ning frequencies over a wide range. For example, the resistors 9, shown connected in by the switch 8, may be of such size that the master pulse frequency on leads |4 and |4' is 31.5 kc. By changing the switch 8 to connect other resistors 9the frequency can be quickly changed to values predetermined by the size of the resistors.

In Fig. 3, lead 45 connects from oscillator 25 to a carrier generator 4| and to a horizontal super-synchronizing shaping device 42. A lead 43 connects the generator 4| to a keying tube 44. A lead 45. also connects fromv oscillator 33 to keying tube 44. A lead 46 connects keying tube 44 to the mixer 4l so that the frequencies of the oscillators 3| and 33 are applied to this mixer 41. Switch 48'and resistance 49 are for partly short-circuiting the keying tube 44, thus allowing the signal from generator 4| to appear at the mixer 41 continuously in a weak form and to be keyed to full strength by the signals from oscillator 33.

The mixer 4? is also adapted to another type of signal so that when the switch 52 is closed a signal is introduced from the divider stage 3| of Fig. 3. By closing the switch 48 a small amount of carrier frequency generated in 4| is introduced into the composite super synchronizing signal which is delivered from 53 to the remaining television equipment. In practice this approximately 500 kilocycle signal which in the instance of the specific frequencies illustrated in Fig. 3'W0uld be 535.5 kilocycles, is keyed into the composite synchronizing signal for a short interval at eld frequency periodicity by pulses from the divider stage 33 of Fig. 3. The box 4| consists of two multiplier stages which increase .the line frequency pulses from box 25 to an exact harmonic which in the case illustrated is the 34thV harmonic. Then, by introducing a small amount of this 34th harmonic signal which is at a frequeucy of 535.5 kc. (15.75 kc. 34) into the mixer 4l and then into the composite supersynchronizing illustrated at box 53, and applying the same to a television receiver the pattern will be such that each line will have a modulation of 34 bright and dark bars. The number of bars of course vary according to the particular scanning combination that is chosen. The closing of switch 48 therefore causes uniform interval markings to appear as vertical lines and consequently a television receiver tube will have a calibration of its linearity in the horizontal direction.

When the switch 52 is closed impulses from the divider stage 3| of Fig. 3 are introduced into the television receiver as indicated by the groups 59 of lines as shown in Fig. 4. The lead 54 comes from the connection in box 3| which corresponds to the connection between transformer winding I5 and condenser ll of Fig. 2 except that the connection is the corresponding one in the divider tube in box 3|. By choosing'this picko point .the wire 54wil1 contain signals for example of 900 C. P. S. of large intensity generated directly by the relaxation oscillator of the divider stage 3| and also there will be present the weaker signals which are fed to that point for synchronizing purposes from the earlier divider stage 30 having a frequency of 900 C. P. S. The strong signals will occur at 900 C. P. S. or once for every 35th oscillation (1/7 of 1/5 of 31.5 kc. in the case illustrated) of the master pulse oscillator 24. vThe weaker pulses which are fed through from the box 30 to synchronize the oscillator of 3| will occur five times as often, or at 1/7 of 31.5 kc., or 4500 C. P. S. Thus there are strong equally spaced impulses |56 between which four weaker impulses 65 occur. In Fig. 3 the master pulse oscillator 24 is assumed to be running at 31.5 kilocycles. Y

A first divider stage 30l divides this frequency by a factor of 'l and the second divider stage 3| divides further by a factor of 5. Since the divider 25 which delivers the line frequency pulses operates at half the frequency of the master oscillator 24, the master oscillator 24applies impulses at every half line of scanning. Therefore the 4500 C. P. S. impulses which are fed to wire 54 by the synchronizing action of,- box 30 places impulses every 'th half line of scanning, since the linefnscanning frequency 15,750+4500=1/2 of '7,`

and' the stronger 900 C. P. S. impulses supplied by divider 3l to wire 54 put an indicator mark on every 35th half line since 15,750+900=1/2 of 35. The result of `this signal when switch 52 is closed gives an appearance on the receiving tube screen as shown in Fig. 4. There will be a series of calibration markings down the center of the television picture and another series of calibration markings at the ends of the lines or at the edges of ,the picture since the markings at the ends of the lines are supplied because of the rapid return time.

In Fig. 4 reference character 56 represents the horizontal dimension of a received television picture which is four units wide in comparison with the vertical dimension 51 which is three units high. For the linearity tests the receiving tube may either have a picture upon which the linearity test calibrations are superposed, or the transmitter may be sending an artificial white ileld upon which the linearity test calibrations appear visibly.

Closing of the switch 48 (Fig. 3) introduces on'the pattern of Fig. 4 the 34th harmonic 535.5 kc., for example, of the line frequency 15.75 kc. This results in the dark vertical stripes 59 separated by the light vertical stripes 60. Approximately 30 of these dark vertical stripes 59 would be visible across the pattern since the remaining 4 occur on the return trace which is blanked out. in time, they would appear uniformly spaced n the vreceiving screen only when the horizontal linearity is correct. Thus the receiver scanning may be checked for linearity and may be adjusted by use of these bars or stripes 59.

When the picture test pattern is placed on the transmitting camera its linearity can be checked independently by comparing the line markings of the test pattern with these uniform time interval markings 59 as seen on the receiving tube screen, Fig. 4. Furthermore, if the receiver should be non-linear it is still possible to adjust accurately the transmitting camera linearity independently and thus avoid the difficulty which has been encountered in the past whereby a pattern might be reproduced on the receiver with apparent linearity which in fact Since these vertical bars occur uniformly' was a combination of a non-linear error at the transmitter camera and a. corresponding corrective non-linearity at the receiver. By this method of testing linearity it is possible to ad. just the absolute linearity of the transmitter camera independently of the adjustment of linearity of the receiver scanning.

In Fig. 4 reference character 62 indicates a linearity calibration down the center of the picture which will be introduced bythe closing of switch 52 of Fig. 3. This calibration appears as a series of fine lines every fifth one of which is introduced as shown at 66 as a heavy line due to the dividing action of 5:1 between boxes 30 and 3l of Fig. 3, in the particular example illustrating this invention. In any combination of line and field scanning there will be at the box 3l of Fig. 3 a signal available to give evenly spaced indicating calibrations. 'Iime can therefore be used for checking vertical linearity and if the vertical scanning, for example, tends to be slower at the top than in the middle these calibration marks would appear to be packed at the top. In practice the switches 48 and 52 enable these linearity test signals to be inserted at will. In addition to the calibration strip 62 down the center of the picture there will be calibration indications 61 and 61 caused by the alternate signals provided from divider stage 3|. This indicating strip is actually spread into two parts because of the rapid return of the spot at the receiver horizontal scanning. In this way both horizontal and vertical linearity indications will be given over all the useful regions of the picture area.

What is claimed is:

In a device of the character described, an oscillator for generating a, predetermined frequency, means to control said frequency, a series of frequency dividers connected to said oscillator, and means to obtain a composite signal from said oscillator and one of said frequency dividers in which a mixer is provided for said composite signal, a keying tube is provided between said oscillator and said mixer, and a switch and by-pass resistance is provided across said keying tube.

ROBERT E. KESSLER. 

